http://www.finalfantasyultima.com/ff2.html

I found this site a few minutes ago, and I´ve drawn conclusions from the artwork which jobs the characters are technically intended to have.
I actually think the following party is the correct one:

Frioniel: Paladin
Maria: Black Wizard
Guy: Fighter/Monk
Lionheart: Knight/Swordsman

The reasons?
Frioniel, I think, looks Paladin-ish somehow; he reminds me of Cecil from FF4, with that outfit and stuff.
Also, in the game, it just feels like he´s intended to have skills from both the fighting and healing department;
I dunno why, I got that impression.
Maria has got this darker, "curvy" Black Wizard kind of look, and actually, she starts out with the highest Intelligence. Guy is obviously a Monk or something similar, that´s really, really obvious; I mean - a GIANT with super muscles!
Lionheart looks like this typhical soldier, and he always carries those swords around.
So he´s most likely a pure Knight, no healing abilities but far superior to Frioniel in physical strength.

I like to think of them this way.
It makes sense.